U.S. patent number 10,070,218 [Application Number 14/618,813] was granted by the patent office on 2018-09-04 for class d amplifier chip with duty ratio limiting functions and the device thereof.
This patent grant is currently assigned to SHENZHEN SKYWORTH-RGB ELECTRONIC CO., LTD.. The grantee listed for this patent is SHENZHEN SKYWORTH-RGB ELECTRONIC CO., LTD. Invention is credited to Bingjie Wu, Zhichang Yang, Shijun Zuo.
United States Patent |
10,070,218 |
Zuo , et al. |
September 4, 2018 |
Class D amplifier chip with duty ratio limiting functions and the
device thereof
Abstract
The present invention discloses a class D amplifier chip with
duty ratio limiting functions and the device thereof, a class D
amplifier chip includes triangle wave modules, PWM modulation
modules, duty ratio detection modules and logic control modules,
the input differential audio signals and triangle wave signals
generated by the triangle wave module are converted into low
voltage pulsed PWM signals through the PWM modulation module, then
gets driving processed and generates high voltage pulses; the duty
ratio detection module real-time detects the duty ratio of PWM
signals, when the logic control module decides the duty ratio of
the PWM signals is larger than the preset maximum value, the PWM
module is controlled to stop working, equals to close the audio
output of the class D amplifier device; which limits the amplitude
of the output audio signals, avoids burning the speaker due to an
overlarge amplitude.
Inventors: |
Zuo; Shijun (Shenzhen,
CN), Yang; Zhichang (Shenzhen, CN), Wu;
Bingjie (Shenzhen, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
SHENZHEN SKYWORTH-RGB ELECTRONIC CO., LTD |
Shenzhen |
N/A |
CN |
|
|
Assignee: |
SHENZHEN SKYWORTH-RGB ELECTRONIC
CO., LTD. (Shenzhen, CN)
|
Family
ID: |
50996184 |
Appl.
No.: |
14/618,813 |
Filed: |
September 22, 2014 |
PCT
Filed: |
September 22, 2014 |
PCT No.: |
PCT/CN2014/087028 |
371(c)(1),(2),(4) Date: |
February 10, 2015 |
PCT
Pub. No.: |
WO2015/143852 |
PCT
Pub. Date: |
October 01, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170013358 A1 |
Jan 12, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 28, 2014 [CN] |
|
|
2014 1 0121747 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03K
7/08 (20130101); H03F 3/2173 (20130101); H03F
3/217 (20130101); H04R 3/007 (20130101); H03F
3/185 (20130101); H03F 2200/171 (20130101); H03F
2200/03 (20130101); H03F 2200/426 (20130101); H03F
2200/78 (20130101); H03F 2200/351 (20130101) |
Current International
Class: |
H03F
3/38 (20060101); H03F 3/185 (20060101); H03F
3/217 (20060101); H04R 3/00 (20060101); H03K
7/08 (20060101) |
Field of
Search: |
;330/10,251,207A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Khanh V
Assistant Examiner: Nguyen; Kheim
Attorney, Agent or Firm: Anova Law Group, PLLC
Claims
The invention claimed is:
1. A class D amplifier chip with duty ratio limiting functions,
comprising: a triangle wave module, configured to generate triangle
wave signals, a PWM modulation module, configured to convert a
plurality of input differential audio signals and the triangle wave
signals generated by the triangle wave module into low voltage
pulsed PWM signals, and drive the PWM signals to generate high
voltage pulses; a duty ratio detection module, configured to detect
in real-time a duty ratio of the PWM signals generated by the PWM
modulation module; a logic control module, configured to
immediately shut off the PWM modulation module if the duty ratio of
the PWM signals is larger than a preset maximum value for the duty
ratio; wherein the PWM modulation module comprises a first
resistor, a second resistor, a third resistor, a fourth resistor, a
first amplifier, a first comparator, a second comparator, a first
driving circuit and a second driving circuit; wherein a positive
input node of the first amplifier connects to a first input node
for differential audio signals through the first resistor, and also
connects to an output node of the first driving circuit through the
third resistor, and an inverse input node of the first amplifier
connects to a second input node for the differential audio signals
through the second resistor, and also connects to the output node
of the second driving circuit through the fourth resistor, wherein
a positive output node of the first amplifier connects to an
inverse input node of the first comparator, a negative output node
of the first amplifier connects to an inverse input node of the
second comparator, wherein a plurality of positive input nodes of
both the first comparator and the second comparator connect to an
output node of the triangle wave module, an output node of the
first comparator connects to an input node of the first driving
circuit and to the duty ratio detection module, wherein an output
node of the second comparator connects to an input node of the
second driving circuit and to the duty ratio detection module,
wherein both the output nodes of the first driving circuit and the
second driving circuit are the output node of the class D
amplifier, and both the control nodes of the first driving circuit
and the second driving circuit connect to the logic control
module.
2. The class D amplifier chip with duty ratio limiting functions
according to claim 1, wherein the logic control module comprises: a
first anti-jamming circuit, a second anti-jamming circuit, a third
inverter, a fourth inverter, an OR gate, a nineteenth MOS
transistor, a twentieth MOS transistor, a twenty first MOS
transistor and a twenty second MOS transistor; wherein a gate
electrode of the nineteenth MOS transistor connects to a gate
electrode of the twentieth MOS transistor and to a
charging-discharging control unit, wherein a drain electrode of the
nineteenth MOS transistor connects to a drain electrode of the
twentieth MOS transistor and to an input node of the third
inverter, wherein a source electrode of the twentieth MOS
transistor connects to an input node of the first anti-jamming
circuit, wherein the output node of the third inverter connects to
a control node of the first anti-jamming circuit and to a first
input node of the OR gate; wherein a gate electrode of the twenty
first MOS transistor connects to a gate electrode of the twenty
second MOS transistor and to the charging-discharging control unit,
wherein a drain electrode of the twenty first MOS transistor
connects to a drain electrode of the twenty second MOS transistor
and to the input node of the fourth inverter, wherein a source
electrode of the twenty second MOS transistor connects to an input
node of the second anti-jamming circuit, wherein an output node of
the fourth inverter connects to a control node of the second
anti-jamming circuit and to the second input node of the OR gate;
wherein a plurality of source electrodes of the nineteenth and of
the twenty-first MOS transistors connect to a voltage reference
node, and wherein an output node of the OR gate connects to the PWM
modulation module.
3. The class D amplifier chip with duty ratio limiting functions
according to claim 2, wherein the first anti-jamming circuit
comprises: a twenty-third MOS transistor and a twenty-fourth MOS
transistor, wherein a drain electrode of the twenty-third MOS
transistor connects to a gate electrode of the twenty-third MOS
transistor, wherein the source electrode of the twentieth MOS
transistor connects to a drain electrode of the twenty-fourth MOS
transistor, wherein a gate electrode of the twenty-fourth MOS
transistor connects to an output node of the third inverter, and
wherein a source electrode of the twenty-third MOS transistor and a
source electrode of the twenty-fourth MOS transistors are both
getting grounded.
4. The class D amplifier chip with duty ratio limiting functions
according to claim 2, wherein the second anti-jamming circuit
comprises: a twenty-fifth MOS transistor and a twenty-sixth MOS
transistor, wherein a drain electrode of the twenty-fifth MOS
transistor connects to a gate electrode of the twenty-fifth MOS
transistor, wherein a source electrode of the twenty-second MOS
transistor and a drain electrode of the twenty-sixth MOS
transistor, wherein a gate electrode of the twenty-sixth MOS
transistor connects to an output node of the fourth inverter, and
wherein a source electrode of the twenty-fifth MOS transistor and a
source electrode of the twenty-sixth MOS transistor are both
getting grounded.
5. The class D amplifier chip with duty ratio limiting functions
according to claim 1, wherein the duty ratio detection module
comprises: a mirror current unit, configured to convert an input
bias current into a charging current and discharging current, which
charging current and discharging current is output to the
charging-discharging control unit in a preset ratio; and a
charging-discharging control unit, configured to convert the
charging and discharging currents output from the mirror current
unit into the corresponding capacitor voltages, and then to send
the capacitor voltages to the logic control module, wherein the
output of the charging-discharging control unit corresponds to the
PWM signals generated by the PWM modulation module.
6. The class D amplifier device with duty ratio limiting functions
according to claim 5, wherein the mirror current unit comprises: a
first MOS transistor, a second MOS transistor, a third MOS
transistor, a fourth MOS transistor, a fifth MOS transistor, a
sixth MOS transistor, a seventh MOS transistor, an eighth MOS
transistor, a ninth MOS transistor, a tenth MOS transistor, an
eleventh MOS transistor, a twelfth MOS transistor, a thirteenth MOS
transistor, a fourteenth MOS transistor; and wherein a gate
electrode of the first MOS transistor connects to a drain electrode
of the first MOS transistor, a gate electrode of the third MOS
transistor, a gate electrode of the fifth MOS transistor, and a
gate electrode of the seventh MOS transistor, wherein a source
electrode of the first MOS transistor connects to a drain electrode
of the second MOS transistor, a gate electrode of the second MOS
transistor, a gate electrode of the fourth MOS transistor, a gate
electrode of the sixth MOS transistor, and a gate electrode of the
eighth MOS transistor, wherein a source electrode of the third MOS
transistor connects to a drain electrode of the fourth MOS
transistor, wherein a source electrode of the fifth MOS transistor
connects to a drain electrode of the sixth MOS transistor, wherein
a source electrode of the seventh MOS transistor connects to a
drain electrode of the eighth MOS transistor, wherein a source
electrode of each of the second, fourth, sixth, and eighth MOS
transistor is getting grounded, wherein a drain electrode of the
third MOS transistor connects to a drain electrode of the tenth MOS
transistor, a gate electrode of the tenth MOS transistor, a gate
electrode of the twelfth MOS transistor, and a gate electrode of
the fourteenth MOS transistor, wherein a source electrode of the
tenth MOS transistor connects to a drain electrode of the ninth MOS
transistor, a gate electrode of the ninth electrode, a gate
electrode of the ninth MOS transistor, a gate electrode of the
eleventh MOS transistor, and a gate electrode of the thirteenth MOS
transistor, wherein a source electrode of the twelfth MOS
transistor connects to a drain electrode of the eleventh MOS
transistor, wherein a source electrode of the fourteenth MOS
transistor connects to a drain electrode of the thirteenth MOS
transistor, wherein a source electrode of each of the ninth,
eleventh and the thirteenth MOS transistor connect to a voltage
reference node, wherein a drain electrode of the twelfth MOS
transistor connects to a first input node of the
charging-discharging control unit, wherein a drain electrode of the
fourteenth MOS transistor connects to a second input node of the
charging-discharging control unit, wherein a drain electrode of the
fifth MOS transistor connects to a first output node of the
charging-discharging control unit, and wherein a drain electrode of
the seventh MOS transistor connects to a second output node of the
charging-discharging control unit.
7. The class D amplifier chip with duty ratio limiting functions
according to claim 5, wherein the first MOS transistor, second MOS
transistor, third MOS transistor, fourth MOS transistor, fifth MOS
transistor, sixth MOS transistor, seventh MOS transistor, and
eighth MOS transistor each is a NMOS type transistor, and wherein
the ninth MOS transistor, tenth MOS transistor, eleventh MOS
transistor, twelfth MOS transistor, thirteenth MOS transistor and
fourteenth MOS transistor each is a PMOS type transistor.
8. The class D amplifier chip with duty ratio limiting functions
according to claim 5, wherein the charging-discharging control unit
comprises: a first inverter, a second inverter, a first capacitor,
a second capacitor, a fifteenth MOS transistor, a sixteenth MOS
transistor, a seventeenth MOS transistor, an eighteenth MOS
transistor; wherein an input node of the first inverter connects to
the PWM modulation module, wherein an output node of the first
inverter connects to a gate electrode of the fifteenth MOS
transistor and a gate electrode of the sixteenth MOS transistor,
wherein a source electrode of the fifteenth MOS transistor connects
to a drain electrode of the twelfth MOS transistor, wherein a
source electrode of the sixteenth MOS transistor connects to a
drain electrode of the fifth MOS transistor, wherein one end of a
first capacitor connects to a drain electrode of the fifteenth MOS
transistor and a drain electrode of the sixteenth MOS transistor,
and the other end of the first capacitor gets grounded, wherein an
input node of the second inverter connects to the PWM modulation
module, wherein an output node of the second inverter connects to a
gate electrode of the seventeenth MOS transistor and the eighteenth
MOS transistor, wherein a source electrode of the seventeenth MOS
transistor connects to a drain electrode of the fourteenth MOS
transistor, wherein a source electrode of the eighteenth MOS
transistor connects to a drain electrode of the seventh MOS
transistor, wherein one end of the second capacitor connects to a
drain electrode of the seventeenth MOS transistor and a drain
electrode of the eighteenth MOS transistor, and the other end of
the second capacitor gets grounded.
9. The class D amplifier chip with duty ratio limiting functions
according to claim 5, wherein the logic control module comprises: a
first anti-jamming circuit, a second anti-jamming circuit, a third
inverter, a fourth inverter, an OR gate, a nineteenth MOS
transistor, a twentieth MOS transistor, a twenty first MOS
transistor and a twenty second MOS transistor; wherein a gate
electrode of the nineteenth MOS transistor connects to a gate
electrode of the twentieth MOS transistor and the
charging-discharging control unit, wherein a drain electrode of the
nineteenth MOS transistor connects to a drain electrode of the
twentieth MOS transistor and an input node of the third inverter,
wherein a source electrode of the twentieth MOS transistor connects
to an input node of the first anti-jamming circuit, wherein an
output node of the third inverter connects to a control node of the
first anti-jamming circuit and a first input node of the OR gate;
wherein a gate electrode of the twenty first MOS transistor
connects to a gate electrode of the twenty second MOS transistor
and the charging-discharging control unit, wherein a drain
electrode of the twenty first MOS transistor connects to a drain
electrode of the twenty second MOS transistor and an input node of
the fourth inverter, wherein a source electrode of the twenty
second MOS transistor connects to an input node of the second
anti-jamming circuit, wherein an output node of the fourth inverter
connects to a control node of the second anti-jamming circuit and a
second input node of the OR gate; wherein a source electrodes of
the nineteenth MOS transistor and the twenty-first MOS transistor
connect to the voltage reference node, and wherein an output node
of the OR gate connects to the PWM modulation module.
10. The class D amplifier chip with duty ratio limiting functions
according to claim 9, wherein the first anti-jamming circuit
comprises a twenty-third MOS transistor and a twenty-fourth MOS
transistor, wherein a drain electrode of the twenty-third MOS
transistor connects to a gate electrode of the twenty-third MOS
transistor, wherein a source electrode of the twentieth MOS
transistor connects to a drain electrode of the twenty-fourth MOS
transistor, wherein a gate electrode of the twenty-fourth MOS
transistor connects to an output node of the third inverter, and
wherein a source electrode of the twenty-third MOS transistor and a
source electrode of the twenty-fourth MOS transistor are both
getting grounded.
11. The class D amplifier chip with duty ratio limiting functions
according to claim 9, wherein the second anti-jamming circuit
comprises a twenty-fifth MOS transistor and a twenty-sixth MOS
transistor, wherein a drain electrode of the twenty-fifth MOS
transistor connects to a gate electrode of the twenty-fifth MOS
transistor, wherein a source electrode of the twenty-second MOS
transistor and a drain electrode of the twenty-sixth MOS
transistor, wherein a gate electrode of the twenty-sixth MOS
transistor connects to an output node of the fourth inverter, and
wherein a source electrode of the twenty-fifth MOS transistor and a
source electrode of the twenty-sixth MOS transistor are both
getting grounded.
12. A class D amplifier device with duty ratio limiting functions,
comprising: a filter, a speaker and a class D amplifier chip with
duty ratio limiting functions, wherein the class D amplifier chip
comprises: a triangle wave module, configured to generate triangle
wave signals, a PWM modulation module, configured to convert a
plurality of input differential audio signals and the triangle wave
signals generated by the triangle wave module into low voltage
pulsed PWM signals, and drive the PWM signals to generate high
voltage pulses output; a duty ratio detection module, configured to
detect in real-time a duty ratio of the PWM signals generated by
the PWM modulation module; a logic control module, configured to
immediately shut off the PWM modulation module if the duty ratio of
the PWM signals is larger than a preset maximum value, wherein the
PWM modulation module comprises a first resistor, a second
resistor, a third resistor, a fourth resistor, a first amplifier, a
first comparator, a second comparator, a first driving circuit and
a second driving circuit; wherein a positive input node of the
first amplifier connects to a first input node for differential
audio signals through the first resistor, and also connects to an
output node of the first driving circuit through the third
resistor, and an inverse input node of the first amplifier connects
to a second input node for the differential audio signals through
the second resistor, and also connects to the output node of the
second driving circuit through the fourth resistor, wherein a
positive output node of the first amplifier connects to an inverse
input node of the first comparator, a negative output node of the
first amplifier connects to an inverse input node of the second
comparator, wherein a plurality of positive input nodes of both the
first comparator and the second comparator connect to an output
node of the triangle wave module, an output node of the first
comparator connects to an input node of the first driving circuit
and to the duty ratio detection module, wherein an output node of
the second comparator connects to an input node of the second
driving circuit and to the duty ratio detection module, wherein
both the output nodes of the first driving circuit and the second
driving circuit are the output node of the class D amplifier, and
both the control nodes of the first driving circuit and the second
driving circuit connect to the logic control module, and wherein
the class D amplifier chip connects to the speaker through the
filter, and the high voltage pulses output from the class D
amplifier chip is restored into audio signals after being filtered
by the filter and before an output to the speaker is generated
causing it to vibrate and provide audio.
Description
FIELD OF THE INVENTION
The present invention relates to the field of technologies on power
supplies, and more particularly, to a class D amplifier chip with
duty ratio limiting functions and the device thereof.
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of PCT patent application no.
PCT/CN2014/087028 filed on Sep. 24, 2014 and Chinese patent
application no. 201410121747.2 filed on Mar. 28, 2014 the entire
contents of all of which are incorporated herein by reference.
BACKGROUND
Class D amplifier (i.e., class D audio power amplifier) is a
switching type power amplifier, which has the advantage of high
efficiency and less heat generating, it has been widely applied to
the field of consumer electronic products area, including
intelligent TVs, intelligent cell phones and more. Referring to
FIG. 1, commonly seen class D amplifiers (Inside the dashed box in
FIG. 1, it is the internal structure of a class D amplifier,)
include: Amplifier a (AMPa), Comparator a (CMPa), Comparator b
(CMPb), Driver a and Driver b; their connection relationship is
shown in FIG. 1. The operating principle of this class D amplifier
is based on PWM (Pulse Width Modulation) mode: differential audio
signals are amplified by the amplifier AMPa, then input into the
comparators CMPa and CMPb in two routes separately, after comparing
with the input triangle wave signals, two routes of PWM signals are
achieved respectively, then the amplitudes of the two routes of PWM
signals are amplified when passing through the driver a and driver
b separately; finally, they are filtered and restored into audio
signals, which drive the speaker to vibrate and give out
voices.
When the amplitude of the input differential audio signals is
overlarge, it could make the amplitude of the restored audio
signals exceed the power rating of the speaker, or cause short
circuit to the capacitor for input, Ca or Cb, resulting in making
the restored audio signals a DC component, which could burn the
speaker out. In order to avoid this kind of anomalies happen, the
output amplitude of the class D amplifier needs to be restricted.
Since the pulse width of the PWM signals, (i.e., the duty ratio) is
proportional to the audio signal amplitude, therefore, it is
possible to restrict the amplitude of the audio signals for output
by limiting the duty ratio of the PWM signals.
BRIEF SUMMARY OF THE DISCLOSURE
The technical problem to be solved in the present invention, aiming
at the defects of the prior art, provides a class D amplifier chip
with duty ratio limiting functions and the device thereof, in order
to solve the problem in the prior art, that is, the class D
amplifiers in the prior art are not able to restrict the output
amplitude of audio signals, and, when the duty ratio of the PWM
signals is overlarge, the speaker could get burnt out.
The technical solution of the present invention to solve the said
technical problems is as follows: a class D amplifier chip with
duty ratio limiting functions, wherein, comprising a triangle wave
module, configured to generate triangle wave signals; a PWM
modulation module, configured to convert the input differential
audio signals and the triangle wave signals generated by the said
triangle wave module into low voltage pulsed PWM signals, drive the
said PWM signals and generate high voltage pulses; a duty ratio
detection module, configured to real-time detect the duty ratio of
the PWM signals generated by the said PWM modulation module; a
logic control module, configured to control the PWM modulation
module stop working while deciding the duty ratio of the PWM
signals is larger than the preset maximum value.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the said PWM modulation module comprises a first resistor,
a second resistor, a third resistor, a fourth resistor, a first
amplifier, a first comparator, a second comparator, a first driving
circuit and a second driving circuit; the positive input node of
the said first amplifier connects to the first input node for
differential audio signals through the first resistor, it also
connects to the output node of the first driving circuit through
the third resistor, and the inverse input node of the first
amplifier connects to the second input node for the differential
audio signals through the second resistor, as well as the output
node of the second driving circuit through the fourth resistor, the
positive output node of the first amplifier connects to the inverse
input node of the first comparator, the negative output node of the
first amplifier connects to the inverse input node of the second
comparator, the positive input nodes of both the said first
comparator and the second comparator connect to the output node of
the triangle wave module, the output node of the first comparator
connects to the input node of the first driving circuit and the
duty ratio detection module, the output node of the second
comparator connects to the input node of the second driving circuit
and the duty ratio detection module, both output nodes of the first
driving circuit and the second driving circuit are output node of
the class D amplifier, both control nodes of the first driving
circuit and the second driving circuit connect to the logic control
module.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the said duty ratio detection module comprises: a mirror
current unit, configured to convert the input bias current into
charging current and discharging current following the preset
ratio, then send to the charging-discharging control unit; a
charging-discharging control unit, configured to output
charging-discharging commands, according to the PWM signals
generated by the said PWM modulation module, convert the charging
and discharging currents output from the said mirror current unit
into the according capacitor voltages before sending to the logic
control module.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the said mirror current unit comprises: a first MOS
transistor, a second MOS transistor, a third MOS transistor, a
fourth MOS transistor, a fifth MOS transistor, a sixth MOS
transistor, a seventh MOS transistor, an eighth MOS transistor, a
ninth MOS transistor, a tenth MOS transistor, an eleventh MOS
transistor, a twelfth MOS transistor, a thirteenth MOS transistor,
a fourteenth MOS transistor; the gate electrode of the said first
MOS transistor connects to the drain electrode of the first MOS
transistor, the gate electrode of the third MOS transistor, the
gate electrode of the fifth MOS transistor, and the gate electrode
of the seventh MOS transistor, the source electrode of the first
MOS transistor connects to the drain electrode of the second MOS
transistor, the gate electrode of the second MOS transistor, the
gate electrode of the fourth MOS transistor, the gate electrode of
the sixth MOS transistor, the gate electrode of the eighth MOS
transistor, the source electrode of the third MOS transistor
connects to the drain electrode of the fourth MOS transistor, the
source electrode of the fifth MOS transistor connects to the drain
electrode of the sixth MOS transistor, the source electrode of the
seventh MOS transistor connects to the drain electrode of the
eighth MOS transistor, while the source electrodes of all the said
second, fourth, sixth, eighth MOS transistors are getting grounded;
the drain electrode of the said third MOS transistor connects to
the drain electrode of the tenth MOS transistor, the gate electrode
of the tenth MOS transistor, the gate electrode of the twelfth MOS
transistor and the gate electrode of the fourteenth MOS transistor,
the source electrode of the said tenth MOS transistor connects to
the drain electrode of the ninth MOS transistor, the gate electrode
of the ninth electrode, the gate electrode of the eleventh MOS
transistor and the gate electrode of the thirteenth MOS transistor,
the source electrode of the twelfth MOS transistor connects to the
drain electrode of the eleventh MOS transistor, the source
electrode of the fourteenth MOS transistor connects to the drain
electrode of the thirteenth MOS transistor, the source electrodes
of the said ninth, eleventh and thirteenth MOS transistors connect
to the voltage reference node, the drain electrode of the said
twelfth MOS transistor connects to the first input node of the
charging-discharging control unit, the drain electrode of the said
fourteenth MOS transistor connects to the second input node of the
charging-discharging control unit, the drain electrode of the said
fifth MOS transistor connects to the first output node of the
charging-discharging control unit, the drain electrode of the said
seventh MOS transistor connects to the second output node of the
charging-discharging control unit.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the said first MOS transistor, second MOS transistor,
third MOS transistor, fourth MOS transistor, fifth MOS transistor,
sixth MOS transistor, seventh MOS transistor, eighth MOS
transistor, are all NMOS type transistors; the said ninth MOS
transistor, tenth MOS transistor, eleventh MOS transistor, twelfth
MOS transistor, thirteenth MOS transistor and fourteenth MOS
transistor are all PMOS type transistors.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the charging-discharging control unit comprises: a first
inverter, a second inverter, a first capacitor, a second capacitor,
a fifteenth MOS transistor, a sixteenth MOS transistor, a
seventeenth MOS transistor, an eighteenth MOS transistor; the input
node of the said first inverter connects to the PWM modulation
module, the output node of the first inverter connects to the gate
electrodes of the fifteenth and sixteenth MOS transistors, the
source electrode of the fifteenth MOS transistor connects to the
drain electrode of the twelfth MOS transistor, the source electrode
of the sixteenth MOS transistor connects to the drain electrode of
the fifth MOS transistor, one end of the said first capacitor
connects to the drain electrodes of the fifteenth and sixteenth MOS
transistors, while the other end of the first capacitor gets
grounded; the input node of the said second inverter connects to
the PWM modulation module, the output node of the second inverter
connects to the gate electrodes of the seventeenth and eighteenth
MOS transistors, the source electrode of the seventeenth MOS
transistor connects to the drain electrode of the fourteenth MOS
transistor, the source electrode of the eighteenth MOS transistor
connects to the drain electrode of the seventh MOS transistor, one
end of the said second capacitor connects to the drain electrodes
of the seventeenth and eighteenth MOS transistors, while the other
end of the second capacitor gets grounded.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the said logic control module comprises: a first
anti-jamming circuit, a second anti-jamming circuit, a third
inverter, a fourth inverter, an OR gate, a nineteenth MOS
transistor, a twentieth MOS transistor, a twenty-first MOS
transistor and a twenty-second MOS transistor; the gate electrode
of the said nineteenth MOS transistor connects to the gate
electrode of the twentieth MOS transistor and the
charging-discharging control unit, the drain electrode of the
nineteenth MOS transistor connects to the drain electrode of the
twentieth MOS transistor and the input node of the third inverter,
the source electrode of the twentieth MOS transistor connects to
the input node of the first anti-jamming circuit, the output node
of the said third inverter connects to the control node of the
first anti-jamming circuit and the first input node of the OR gate
OR; the gate electrode of the said twenty-first MOS transistor
connects to the gate electrode of the twenty-second MOS transistor
and the charging-discharging control unit, the drain electrode of
the twenty-first MOS transistor connects to the drain electrode of
the twenty-second MOS transistor and the input node of the fourth
inverter, the source electrode of the twenty-second MOS transistor
connects to the input node of the second anti-jamming circuit, the
output node of the said fourth inverter connects to the control
node of the second anti-jamming circuit and the second input node
of the OR gate; the source electrodes of the said nineteenth and
twenty-first MOS transistors connect to the voltage reference node,
the output node of the said OR gate connects to the PWM modulation
module.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the said first anti-jamming circuit comprises: a
twenty-third MOS transistor and a twenty-fourth MOS transistor, the
drain electrode of the said twenty-third MOS transistor connects to
the gate electrode of the twenty-third MOS transistor, the source
electrode of the twentieth MOS transistor and the drain electrode
of the twenty-fourth MOS transistor, the gate electrode of the said
twenty-fourth MOS transistor connects to the output node of the
third inverter, the source electrodes of the said twenty-third and
twenty-fourth MOS transistors are both getting grounded.
The said class D amplifier chip with duty ratio limiting functions,
wherein, the said second anti-jamming circuit comprises: a
twenty-fifth MOS transistor and a twenty-sixth MOS transistor, the
drain electrode of the said twenty-fifth MOS transistor connects to
the gate electrode of the twenty-fifth MOS transistor, the source
electrode of the twenty-second MOS transistor and the drain
electrode of the twenty-sixth MOS transistor, the gate electrode of
the said twenty-sixth MOS transistor connects to the output node of
the fourth inverter, the source electrodes of the said twenty-fifth
and twenty-sixth MOS transistors are both getting grounded.
A class D amplifier device with duty ratio limiting functions,
wherein, comprising: a filter, a speaker and the said class D
amplifier chip with duty ratio limiting functions, the said class D
amplifier chip connects to the speaker through the filter, high
voltage pulses output from the class D amplifier chip are restored
into audio signals after being filtered by the filter, then output
to the speaker, drive the speaker vibrate and give out voices.
Comparing to the prior technologies, the class D amplifier chip
with duty ratio limiting functions and the device thereof, provided
in the present invention, converts the input differential audio
signals and the triangle wave signals generated from the triangle
wave module into low voltage pulsed PWM signals, through the PWM
modulation module, and drive the said PWM signals then generates
high voltage pulses; the present invention real-time detects the
duty ratio of the said PWM signals, through the duty ratio
detection module, when the logic control module decides the duty
ratio of the PWM signals is larger than the preset maximum duty
ratio, it will control the PWM modulation module stop working, shut
down the output of high voltage pulses from the class D amplifier
chip, that equals to turn off the audio output from the class D
amplifier device; it restricts the amplitude of the output audio
signals, avoids burning the speaker out due to an overlarge
amplitude of the audio signals, achieves the functions of limiting
audio signals and protecting the speaker.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a circuit diagram of the application of current
class D amplifiers in prior arts;
FIG. 2 illustrates a schematic diagram of the class D amplifier
with duty ratio limiting functions according to an embodiment of
the present invention.
FIG. 3 illustrates a circuit diagram of a duty ratio detection
module in the class D amplifier chip with duty ratio limiting
functions as provided in an embodiment of the present
invention.
FIG. 4 illustrates a schematic diagram for the logic control module
in the class D amplifier chip with duty ratio limiting functions as
provided in an embodiment of the present invention.
FIG. 5 illustrates a waveform diagram for the class D amplifier
chip with duty ratio limiting functions as provided in an
embodiment of the present invention.
DETAILED DESCRIPTION
The present invention provides a class D amplifier chip with duty
ratio limiting functions and the device thereof, in order to make
the purpose, technical solution and the advantages of the present
invention clearer and more explicit, further detailed descriptions
of the present invention are stated here, referencing to the
attached drawings and some embodiments of the present invention. It
should be understood that the detailed embodiments of the invention
described here are used to explain the present invention only,
instead of limiting the present invention.
Aiming at the problem in the prior art that a speaker could be
burnt out when the duty ratio of PWM signals in a class D amplifier
is overlarge, the present invention provides a class D amplifier
with duty ratio limiting functions, which is able to shut down the
output of high voltage pulses when the duty ratio of PWM signals is
larger than the preset maximum duty ratio, through limiting the
maximum duty ratio of PWM signals, that equals to shut down the
audio output from the class D amplifier device, avoids that the
output amplitude of the audio signals is overlarge and burns the
speaker out; when the duty ratio of PWM signals is smaller than the
preset maximum duty ratio, the high voltage pulses output from the
class D amplifier chip will be turned on or kept, which ensures the
class D amplifier work normally.
Referring to FIG. 2, the class D amplifier device with duty ratio
limiting functions as provided in the present invention, includes:
a filter, a speaker and a class D amplifier chip 10 with duty ratio
limiting functions, the said class D amplifier chip 10 connects to
the speaker through the filter. The class D amplifier chip 10
includes a PWM modulation module 100, a duty ratio detection module
200, a logic control module 300 and a triangle wave module 400. The
said PWM modulation module 100, duty ratio detection module 200 and
logic control module 300 are connecting one by one, the said
triangle wave module 400 connects to the PWM modulation module 100,
and the said logic control module 300 connects to the PWM
modulation module 100. The PWM modulation module 100 converts the
input differential audio signals and the triangle wave signals
generated by the said triangle wave module into low voltage pulsed
PWM signals, and drive the said PWM signals to generate high
voltage pulses, followed by filtered through the filter and
restored to audio signals then output to the speaker, drives the
speaker vibrating and giving out voices. When the PWM modulation
module 100 is working, the duty ratio detection module 200
real-time detects the duty ratio of the said PWM signals. When the
logic control module 300 decides the duty ratio of the PWM signals
is larger than the preset maximum duty ratio, it controls the PWM
modulation module 100 stop working, and shuts down the high voltage
pulses output from the class D amplifier chip, which equals to turn
off the audio output from the said class D amplifier device, and
avoid burning the speaker out due to an overlarge amplitude of the
audio signals output; when the duty ratio of PWM signals is smaller
than the preset maximum duty ratio, the logic control module 300
will not get started, thus the PWM modulation module 100 works
normally, ensures the audio signals output normally. Wherein, the
said triangle wave module 400 belongs to the current technology,
thus it will not be described here in details.
It should be understood that, the said differential audio signals
input into the PWM modulation module 100 in two routes. And the
said PWM modulation module 100 includes a first resistor R1, a
second resistor R2, a third resistor R3, a fourth resistor R4, a
first amplifier AMP, a first comparator CMP1, a second comparator
CMP2, a first driving circuit and a second driving circuit. The
positive input node of the said first amplifier AMP connects to the
first input node A for differential audio signals through the first
resistor R1, (configured to input the differential audio signals),
it also connects to the output node of the first driving circuit
through the third resistor R3, and the inverse input node of the
first amplifier AMP connects to the second input node B for
differential audio signals through the second resistor R2, as well
as the output node of the second driving circuit through the fourth
resistor R4, the positive output node of the first amplifier AMP
connects to the inverse input node of the first comparator CMP1,
the negative output node of the first amplifier AMP connects to the
inverse input node of the second comparator CMP2, the positive
input nodes of both the said first comparator CMP1 and the second
comparator CMP2 connect to the output node of the triangle wave
module (configured to receive the triangle wave signals), the
output node of the first comparator CMP1 connects to the input node
of the first driving circuit and the duty ratio detection module
200, the output node of the second comparator CMP2 connects to the
input node of the second driving circuit and the duty ratio
detection module 200, both the output node of the first driving
circuit (i.e., the first output node C of the said class D
amplifier chip 10) and the output node of the second driving
circuit (i.e., the second output node D of the said class D
amplifier chip 10) are the output nodes of the class D amplifier
chip 10, and both are connecting to the filter, the control nodes
of both the first driving circuit and the second driving circuit
are connecting to the output node of the logic control module
300.
The first amplifier AMP of the PWM modulation module 100 amplifies
the differential audio signals and outputs inverse shaped sp
signals and sn signals. The sp signals and sn signals are compared
with the input fixed frequency triangle wave signals through the
first comparator CMP1 and the second comparator CMP2 separately,
then two routes of PWM signals with complementary duty ratios (low
voltage pulses) are output, that is, PWMP signals and PWMN signals
(if the duty ratio of PWMP signals is 60%, then that of the PWMN
signals is 40%). The first driving circuit and the second driving
circuit driving process the PWMP signals and PWMN signals
respectively, and generate two routes of according high voltage
pulses, which are then filtered by the filter and restored into two
groups of according audio signals before sending to the speaker.
The duty ratio detection module 200 in the present embodiment is
applied to detect the duty ratios of the PWMP signals and the PWMN
signals.
In specific implementations, the duty ratio detection module 200
adopts a preset current to charge and discharge the capacitor, and
shows the duty ratio of the PWM signals by the ratio of the
charging and discharging currents. Thus the said preset maximum
duty ratio may be expressed in currents as:
Idischarge/(Icharge+Idischarge), wherein, Icharge is the charging
current to the capacitor, and Idischarge is the discharging current
to the capacitor. Duty ratio detection module 200 converts the high
and low electric levels of the PWM signals into the charging and
discharging currents to the capacitor, thus detects the duty
ratio.
Referring to FIG. 3 together, in order to achieve the conversion
between the duty ratio and electric currents, the said duty ratio
detection module 200 includes a mirror current unit and a
charging-discharging control unit 201. The said
charging-discharging control unit 201 connects to the mirror
current unit, the logic control module, as well as the output nodes
of the first comparator CMP1 and the second comparator CMP2 in the
PWM modulation module. The mirror current unit adopts a mirror
current source technology, following the preset ratio, converts the
input bias current Ibias into the charging and discharging
currents, then sends to the charging-discharging control unit 201,
the charging and discharging control unit 201 then outputs the
according charging and discharging commands, following the PWM
signals generated by the said PWM modulation module, and converts
the charging and discharging currents output from the said mirror
current unit into the according values of capacitor voltages and
sends to the logic control module 300. The logic control module 300
decides the values of the duty ratio of the PWM signals, comparing
to the value of the preset maximum duty ratio, based on the said
charging and discharging voltages.
Wherein, the said mirror current unit includes: a first MOS
transistor M1, a second MOS transistor M2, a third MOS transistor
M3, a fourth MOS transistor M4, a fifth MOS transistor M5, a sixth
MOS transistor M6, a seventh MOS transistor M7, an eighth MOS
transistor M8, a ninth MOS transistor M9, a tenth MOS transistor
M10, an eleventh MOS transistor M11, a twelfth MOS transistor M12,
a Thirteenth MOS transistor M13, a fourteenth MOS transistor M14.
The said first MOS transistor M1, second MOS transistor M2, third
MOS transistor M3, fourth MOS transistor M4, fifth MOS transistor
M5, sixth MOS transistor M6, seventh MOS transistor M7, eighth MOS
transistor M8, are all NMOS transistors; while the said ninth MOS
transistor M9, tenth MOS transistor M10, eleventh MOS transistor
M11, twelfth MOS transistor M12, thirteenth MOS transistor M13,
fourteenth MOS transistor M14 are all PMOS transistors.
The gate electrode of the said first MOS transistor M1 connects to
the drain electrode of the first MOS transistor M1, the gate
electrode of the third MOS transistor M3, the gate electrode of the
fifth MOS transistor M5, and the gate electrode of the seventh MOS
transistor M7, the source electrode of the first MOS transistor M1
connects to the drain electrode of the second MOS transistor M2,
the gate electrode of the second MOS transistor M2, the gate
electrode of the fourth MOS transistor M4, the gate electrode of
the sixth MOS transistor M6, the gate electrode of the eighth MOS
transistor M8, the source electrode of the third MOS transistor M3
connects to the drain electrode of the fourth MOS transistor M4,
the source electrode of the fifth MOS transistor M5 connects to the
drain electrode of the sixth MOS transistor M6, the source
electrode of the seventh MOS transistor M7 connects to the drain
electrode of the eighth MOS transistor M8, the source electrode of
the third MOS transistor M3 connects to the drain electrode of the
fourth MOS transistor M4, the source electrode of the fifth MOS
transistor M5 connects to the drain electrode of the sixth MOS
transistor M6, the source electrode of the seventh MOS transistor
M7 connects to the drain electrode of the eighth MOS transistor M8,
while the source electrodes of all the said second, fourth, sixth,
eighth MOS transistors (M2, M4, M6, M8) are all getting grounded;
the drain electrode of the said third MOS transistor M3 connects to
the drain electrode of the tenth MOS transistor M10, the gate
electrode of the tenth MOS transistor M10, the gate electrode of
the twelfth MOS transistor M12, the gate electrode of the
fourteenth MOS transistor M14, the source electrode of the said
tenth MOS transistor M10 connects to the drain electrode of the
ninth MOS transistor M9, the gate electrode of the ninth MOS
transistor M9, the gate electrode of the eleventh MOS transistor
M11 and the gate electrode of the thirteenth MOS transistor M13;
the source electrode of the twelfth MOS transistor M12 connects to
the drain electrode of the eleventh MOS transistor M11, the source
electrode of the fourteenth MOS transistor M14 connects to the
drain electrode of the thirteenth MOS transistor M13, the source
electrodes of the said ninth, eleventh and thirteenth MOS
transistors (M9, M11 and M13) are all connecting to the voltage
reference node VREF; the drain electrode of the said twelfth MOS
transistor M12 connects to the first input node 1 of the
charging-discharging control unit 201, the drain electrode of the
said fourteenth MOS transistor M14 connects to the second input
node 2 of the charging-discharging control unit 201, the drain
electrode of the said fifth MOS transistor M5 connects to the first
output node 5 of the charging-discharging control unit 201, the
drain electrode of the said seventh MOS transistor M7 connects to
the second output node 6 of the charging-discharging control unit
201.
A bias current (Ibias) is generated by a bias circuit, which is a
present structure and belongs to the prior technology, thus no
details will be listed here. The present embodiment adopts a bias
current Ibias as the current source for the charging and
discharging currents. Following a first preset ratio, through the
first MOS transistor M1 and the second MOS transistor M2, the said
bias current Ibias is mirrored to the third MOS transistor M3 and
the fourth MOS transistor M4, the fifth MOS transistor M5 and the
sixth MOS transistor M6, the seventh MOS transistor M7 and the
eighth MOS transistor M8. The currents coming from the third MOS
transistor M3 and the fourth MOS transistor M4, and passing through
the ninth MOS transistor M9 and the tenth MOS transistor M10, are
mirrored to the eleventh MOS transistor M11 and the twelfth MOS
transistor M12, as well as the thirteenth MOS transistor M13 and
the fourteenth MOS transistor M14, following a second preset ratio.
The said first preset ratio and the second preset ratio are decided
by the width (W) and length (L) of the according MOS transistor,
which could be calculated from known formula, and belongs to the
prior art, thus will not be described here in details.
Meanwhile, the bias current, Ibias, (owns a certain high voltage)
conducts the first MOS transistor M1 up to the eighth MOS
transistor M8, these MOS transistors compose a discharging circuit,
waiting for the discharging command from the charging and
discharging control unit 201. The conduction and grounding of the
third MOS transistor M3 and the fourth MOS transistor M4 lowers the
electric level of the gate electrode of the tenth MOS transistor
M10, therefore conducts the ninth MOS transistor M9, the eleventh
MOS transistor M11 up to the fourteenth MOS transistor M14, turns
on the voltage reference node VREF, and the MOS transistors from
the ninth, M9, up to the fourteenth, M14, compose a charging
circuit, waiting for the charging command from the charging and
discharging control unit 201.
Wherein, the said charging and discharging control unit 201
includes a first inverter NOT1, a second inverter NOT2, a first
capacitor C1, a second capacitor C2, a fifteenth MOS transistor
M15, a sixteenth MOS transistor M16, a seventeenth MOS transistor
M17 and an eighteenth MOS transistor M18; both the said fifteenth
MOS transistor M15 and seventeenth MOS transistor M17 are PMOS
transistors, the sixteenth MOS transistor M16 and eighteenth MOS
transistor M18 are NMOS transistors, the unit of the capacity
values of the first capacitor C1 and the second capacitor C2 is
pF.
The input node of the first inverter NOT1 (i.e., the third input
node 3 of the charging and discharging control unit 201) connects
to the output node of the first comparator CMP1 of the PWM
modulation module 100, the output node of the first inverter NOT1
connects to the gate electrodes of the fifteenth MOS transistor M15
and the sixteenth MOS transistor M16, the source electrode of the
fifteenth MOS transistor M15 (that is, the first input node 1 of
the charging and discharging control unit 201) connects to the
drain electrode of the twelfth MOS transistor M12, the source
electrode of the sixteenth MOS transistor M16 (i.e., the first
output node 5 of the charging and discharging control unit 201)
connects to the drain electrode of the fifth MOS transistor M5, one
end of the said first capacitor C1 (i.e., the third output node 7
of the charging and discharging control unit 201) connects to the
drain electrodes of the fifteenth MOS transistor M15 and the
sixteenth MOS transistor M16, the other end of the first capacitor
C1 gets grounded.
The input node of the said second inverter NOT2 (that is, the
fourth input node 4 of the charging and discharging control unit
201) connects to the output node of the second comparator CMP2 of
the PWM modulation module 100, the output node of the second
inverter NOT2 connects to the gate electrodes of the seventeenth
MOS transistor M17 and the eighteenth MOS transistor M18, the
source electrode of the seventeenth MOS transistor M17 (i.e., the
second input node 2 of the charging and discharging control unit
201) connects to the drain electrode of the fourteenth MOS
transistor M14, the source electrode of the eighteenth MOS
transistor M18 (i.e., the second output node 6 of the charging and
discharging control unit 201) connects to the drain electrode of
the seventh MOS transistor M7, one end of the said second capacitor
C2 (that is, the fourth output node 8 of the charging and
discharging control unit 201) connects to the drain electrodes of
the seventeenth MOS transistor M17 and the eighteenth MOS
transistor M18. The other end of the second capacitor C2 gets
grounded.
In the present embodiment, the circuit composed by the first
inverter NOT1, the first capacitor C1, the fifteenth MOS transistor
M15 and the sixteenth MOS transistor M16, expresses the duty ratio
of the PWMP signals in the way of charging and discharging
currents. The work principles in details are: when the PWMP signal
is in a high electric level, the first inverter NOT1 outputs a low
electric level and conducts the fifteenth MOS transistor M15 while
shuts the sixteenth MOS transistor M16 off, the charging current,
Icharge, provided by the eleventh MOS transistor M11 and the
twelfth MOS transistor M12 after mirroring the bias current Ibias,
passes through the eleventh MOS transistor M11, the twelfth MOS
transistor M12 and the fifteenth MOS transistor M15 in the order,
and charges the first capacitor C1; in order to enter the charging
status, the capacitor voltage CP of the first capacitor C1 rises
gradually. When the PWMP signals is in a low electric level, the
first inverter NOT1 outputs a high electric level and conducts the
sixteenth MOS transistor M16, while shuts off the fifteenth MOS
transistor M15. The discharging current, Idischarge, (provided by
the fifth MOS transistor M5 and the sixth MOS transistor M6) output
from the first capacitor C1, passes through the sixteenth MOS
transistor M16, the fifth MOS transistor M5 and the sixth MOS
transistor M6 and gets grounded, enters a discharging status, the
capacitor voltage CP of the first capacitor C1 drops gradually.
Accordingly, in the present embodiment, the circuit composed by the
second inverter NOT2, the second capacitor C2, the seventeenth MOS
transistor M17 and the eighteenth MOS transistor M18 expresses the
duty ratio of the PWMN signals in the method of charging and
discharging currents; the work principle is the same as that of the
PWMP signals, it is proper to reference to that of the PWMP
described above in specific implementations, and will not be
described again here in details.
It should be understood that, if the capacitor voltage CP can rise
to the highest voltage (close to the voltage VVREF of the voltage
reference source VREF) or not, during the charging process, depends
on the ratio of the charging and discharging currents, and the
amount of the duty ratio of the PWMP signals. If the charging and
discharging currents are equal, as long as the duty ratio is larger
than 50%, the first capacitor C1 will keep being charged, up to the
highest voltage; if the duty ratio is lower than 50%, the first
capacitor C1 will keep being discharged until reaches the lowest
voltage.
If the charging and discharging currents are not equal, suppose the
charging current is Icharge and the discharging current is
Idischarge, the critical point of the detected duty ratio (i.e.,
the preset maximum duty ratio) is calculated as
Idischarge/(Icharge+Idischarge). When the capacitor voltage CP of
the first capacitor C1 and the capacitor voltage CN of the second
capacitor C2 are outputting to the logic control module, usually,
only when the discharging current is greater than the charging
current, can a duty ratio over 50% be detected; otherwise, if the
discharging current is smaller than the charging current, only a
duty ratio smaller than 50%% can be detected, in such a case, the
class D amplifier chip 10 will keep having no output. That is due
to the complementation between the duty ratio of the PWMP signal
and the PWMN signal, so there is always one duty ratio, among these
two signals, larger than 50%, resulting in triggering the logic
control module 300 output an enable signal EN. It is possible to
adjust the maximum duty ratio for detection through adjusting the
ratio of the charging and discharging currents.
The capacitor voltage CP of the first capacitor C1 and the
capacitor voltage CN of the second capacitor C2 are input into the
logic control module 300 for further judgments. Referring to FIG. 4
together, the said logic control module 300 includes: a first
anti-jamming circuit 301, a second anti-jamming circuit 302, a
third inverter NOT3, a fourth inverter NOT4, an OR gate OR, a
nineteenth MOS transistor M19, a twentieth MOS transistor M20, a
twenty-first MOS transistor M21 and a twenty-second MOS transistor
M22. Both the said nineteenth MOS transistor M19 and twenty-first
MOS transistor M21 are PMOS transistors, both the twentieth MOS
transistor M20 and the twenty-second MOS transistor M22 are NMOS
transistors.
The gate electrode of the said nineteenth MOS transistor M19
connects to the gate electrode of the twentieth MOS transistor M20
and one end of the first capacitor C1 in the charging and
discharging control unit 201, the drain electrode of the nineteenth
MOS transistor M19 connects to the drain electrode of the twentieth
MOS transistor M20 and the input node of the third inverter NOT3,
the source electrode of the twentieth MOS transistor M20 connects
to the input node 1 of the first anti-jamming circuit 301, the
output node of the said third inverter NOT3 connects to the control
node 2 of the first anti-jamming circuit 301 and the first input
node of the OR gate OR.
The gate electrode of the said twenty-first MOS transistor M21
connects to the gate electrode of the twenty-second MOS transistor
M22 and one end of the second capacitor C2 in the charging and
discharging control unit 201, the drain electrode of the
twenty-first MOS transistor M21 connects to the drain electrode of
the twenty-second MOS transistor M22 and the input node of the
fourth inverter NOT4, the source electrode of the twenty-second MOS
transistor M22 connects to the input node 3 of the second
anti-jamming circuit 302, the output node of the fourth inverter
NOT4 connects to the control node 4 of the second anti-jamming
circuit 302 and the second input node of the OR gate OR.
Both the said source electrodes of the nineteenth MOS transistor
M19 and the twenty-first MOS transistor M21 connect to the voltage
referencing source node VREF, the output node of the said OR gate
OR connects to the control node of the first driving circuit, the
control node of the second driving circuit, the control node of the
first comparator, CMP1, the control node of the second comparator,
CMP2, and the control node of the first amplifier AMP, in the PWM
modulation module.
In the present embodiment, the reverse voltage of the twentieth MOS
transistor M20 and the twenty-second MOS transistor M22 is set to
be VVREF/2. When the capacitor voltage CP of the first capacitor C1
or the capacitor voltage CN of the second capacitor C2 is in a high
electrical level and greater than VVREF/2, either the twentieth MOS
transistor M20 or the twenty-second MOS transistor M22 will be
conducted, and finally outputs an enable signal EN in a high
electric level, therefore, shuts off the first driving circuit, the
second driving circuit, the first comparator CMP1, the second
comparator CMP2 and the first amplifier AMP, then stops the output
of audio signals with relatively large amplitude, avoids burning
the speaker off.
Wherein, the said first anti-jamming circuit 301 includes a
twenty-third MOS transistor M23 and a twenty-fourth MOS transistor
M24; the drain electrode of the said twenty-third MOS transistor
M23 (i.e., the input node 1 of the first anti-jamming circuit 301)
connects to the gate electrode of the twenty-third MOS transistor
M23, the source electrode of the twentieth MOS transistor M20 and
the drain electrode of the twenty-fourth MOS transistor M24, the
gate electrode of the said twenty-fourth MOS transistor M24 (i.e.,
the control node 2 of the first anti-jamming circuit 301) connects
to the output node of the third inverter NOT3, both source
electrodes of the said twenty-third MOS transistor M23 and the
twenty-fourth MOS transistor M24 are getting grounded.
Accordingly, the said second anti-jamming circuit 302 includes a
twenty-fifth MOS transistor M25 and a twenty-sixth MOS transistor
M26; the drain electrode of the said twenty-fifth MOS transistor
M25 (i.e., the input node 3 of the second anti-jamming circuit 302)
connects to the gate electrode of the twenty-fifth MOS transistor
M25, the source electrode of the twenty-second MOS transistor M22
and the drain electrode of the twenty-sixth MOS transistor M26, the
gate electrode of the said twenty-sixth MOS transistor M26 (i.e.,
the control node 4 of the second anti-jamming circuit 302) connects
to the output node of the fourth inverter NOT4, both source
electrodes of the said twenty-fifth MOS transistor M25 and the
twenty-sixth MOS transistor M26 are getting grounded.
In the present embodiment, when the capacitor voltage CP of the
first capacitor C1 is in a low electric level, the nineteenth MOS
transistor M19 gets conducted and outputs a high electric level,
which passes through the third inverter NOT3 and gets inversed,
then output to the OR gate OR, as a low electric level; now the
output results of the OR gate OR are decided by the output of the
fourth inverter NOT4. When either of the input to the OR gate OR is
in a high electric level, it outputs a high electric level; only
when both input are in a low electric level, will it output a low
electric level.
When the capacitor voltage CP of the first capacitor C1 is in a
high electric level and larger than VVREF/2, the twentieth MOS
transistor M20 gets conducted. Due to the gate electrode of the
twenty-third MOS transistor M23 connecting to its drain electrode,
the twenty third MOS transistor M23 is equivalent to a diode (with
a voltage drop of 0.7V), whose anode connects to the source
electrode of the twentieth MOS transistor M20, and the cathode gets
grounded. Thus, when the twentieth MOS transistor M20 gets
conducted, the diode (i.e., the twenty third MOS transistor M23)
also gets conducted, and lowers the input node of the third
inverter NOT3, then the third inverter NOT3 outputs a high electric
level to the OR gate OR, and the OR gate OR outputs a high electric
level. At the same while, the third inverter NOT3 outputs a high
electric level and controls the twenty-fourth MOS transistor M24
conduct, which makes the twenty-third MOS transistor M23
short-circuit, as long as the capacitor voltage CP is keeping in a
high electric level, the third inverter NOT3 is then ensured to
keep outputting a high electric level, which effectively solves the
problem of wave form shaking of the capacitor voltage CP, or
unstable output due to the appearing of interference burrs.
The work principle of the said second anti-jamming circuit 302 is
the same as that of the first anti-jamming circuit 301, thus will
not be described here again.
In order to reduce any mistaken judgments, a time-delay circuit
could be further added after the OR gate OR, that is, the output
node of the said OR gate OR connects to the input node of the
time-delay circuit, and whose output node connects to the control
nodes of the first driving circuit, the second driving circuit, the
first comparator CMP1, the second comparator CMP2 and the first
amplifier AMP; which makes the enable signals EN in the high
electric level delay for 100 ms before outputting. The said
time-delay circuit belongs to the current technology, has multiple
realization methods, as long as it can make the enable signals EN
in high electric levels delay for a certain time before outputting,
thus its detailed circuit structure will not be restricted
here.
Referring to FIG. 5 together, it can be seen after waveform
simulating to the above said class D amplifier chip, supposing the
duty ratio of the PWMP signals is 70%. The high electric level of
the PWMP signals is kept for a relatively long time, thus the
charging time to the first capacitor C1 (that is, the high electric
level time of the PWMP signals) is longer than the discharging time
(that is, the low electric level time of the PWMP signals); in the
present embodiment, the Idischarge/Icharge=2, which means, the
preset maximum duty ratio for detection is 66.7%. Thus, when a PWMP
signal with a duty ratio of 70% is input, the maximum voltage that
the value of the capacitor voltage CP can finally reach is VVREF.
Since the duty ratio of the PWMN signals adding that of the PWMP
signals equals to 100%, thus, the duty ratio of the PWMN signals is
30%. The final value of the capacitor voltage CN is zero. Input the
capacitor voltage CP and the capacitor voltage CN into the logic
control modules, then output the I5_out signal, after some time
delay, the electric level of the I5_out signal changes from low to
high, thus, output the enable signal EN which is high electric
level, therefore, shuts down the output of high voltage pulses, and
protects the speaker.
Additionally, when the amplitude of the differential audio signals
is overlarge, the capacitors for input (i.e., the two capacitors
connecting right after the differential audio signals entrance in
FIG. 2) could be short circuited to the ground. Since the said
class D amplifier device with duty ratio limiting functions is
possible to shut down the output of the class D amplifier chips,
and protect the speaker, when the amplitude of the differential
audio signals is over large. Therefore, when the capacitors for
input is short circuited to the ground, the output of the class D
amplifier chip can also be shut down, thus the said class D
amplifier device can also detect the abnormal situations of short
circuited capacitors for input.
In summary, the class D amplifier chips with duty ratio limiting
functions, as provided in the present invention, and the device
thereof, based on the principle that the output amplitude of the
audio signals is proportional to the duty ratio of the PWM signals,
when deciding that the duty ratio of the PWM signals is larger than
the preset maximum duty ratio, by real-time detecting the duty
ratio of the PWM signals, the PWM modulation module stops working,
and the high voltage pulses output from the class D amplifier chips
is shut down, thus the audio output from the class D amplifier
device is also shut down; while limiting the output with overlarge
duty ratio equals to limiting the output of audio signals with
overlarge amplitudes, thus avoids burning the speaker by audio
signals with overlarge amplitudes. When the duty ratio of the PWM
signals is smaller than the preset maximum duty ratio, the audio
output of the class D amplifier device is turned on or kept, which
ensures the class D amplifier device work normally.
Additionally, the said class D amplifier device can also detect
some abnormal situations, such as: the capacitor for input is short
circuited to the ground.
It should be understood that, the application of the present
invention is not limited to the above examples listed. Ordinary
technical personnel in this field can improve or change the
applications according to the above descriptions, all of these
improvements and transforms should belong to the scope of
protection in the appended claims of the present invention.
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